This application claims the priority of German Application No. 102 19 701.6, filed May 2, 2002, the disclosure of which is expressly incorporated by reference herein.
The present invention is addressed to the transfer of navigation data from navigation transmission facilities to navigation terminals.
U.S. Pat. No. 6,101,178 describes a method for transferring navigation data to navigation terminals in which navigation is transmitted from several navigation data transmission facilities, here from navigation satellites and pseudolites, whereby an interleaving of navigation data of various navigation transmission facilities takes place with a TDMA method.
Such a method is only attained according to the state of the art in that the transmitted navigation data of different navigation data transmission facilities do not mutually disturb one another if possible. This method does not provide for optimization of data transmission to an individual navigation data transmitting facility.
The object of the present invention is to optimize transmission of navigation data from a navigation data transmission facility to navigation terminals.
The present invention provides a method for furnishing and transferring navigation data in a navigation system by transmission of several navigation data blocks from a navigation transmitting facility to navigation terminals. In accordance with the present invention, prior to transmitting navigation data to the navigation terminals, at least two navigation data blocks are interleaved. Basically, any type of distributing and regrouping data of the individual navigation blocks takes place as interleaving, whereby data of different navigation blocks are assembled into a new data packet. The advantage of interleaving is that the data of a data block can be distributed to several data packets, and thus the individual data of the data block can be separated in connection with a data transmission. If during a data transmission a data packet is erroneously transmitted, then not all data of a data block are lost, but rather only part of the data block. The lost part can then possibly be reconstructed on the basis of the remaining data of the data blocks which were transmitted in other data packets.
According to the invention either one or several or all navigation data sending facilities of the navigation system can be implement with such a method, and can also be correspondingly constructed.
The scope of the data with which an interleaving is conducted can be defined by the data content of a data frame (frame) which is ultimately transmitted to the navigation terminal. Generally such a data frame is at least defined by signalization data (headers) and useful data, whereby the signalization data at least contain identification data for identifying the data frame. The scope of the data with which an interleaving is conducted can, however, also be established for a specified transmission time for a navigation data block. A typical transmission time in satellite navigation systems for navigation data blocks which contain navigation reports is, for example, one second.
A transmission time can be established for interleaving, especially for each data unit of the navigation data block, with the aid of an algorithm, whereby the sequence of transmission times deviates from the original sequence of data units within the navigation data block. Thus, an emission of the individual data units of the navigation data blocks is brought about in which the sequence of the data units no longer corresponds to the original sequence of the data units in the navigation data blocks. The meaning of the data units is defined further below.
If there exists a case that at the same time in which a time-uncritical navigation data block is to be transmitted, k time-critical navigation data blocks are also to be sent with k=2, 3, 4 . . . then the algorithm can be constructed in such a way that, for transmitting the k time-critical navigation data blocks with k=2, 3, 4 . . . , and the one time-uncritical navigation data blocks, the transmission times of the data units of each time-critical navigation data block are at all times established in a fraction 1/k of the transmission time of the time-uncritical navigation data block. If, for example, a transmission time of one second is provided for a time-uncritical navigation data block and if at the same time 2 time-critical navigation blocks are to be sent, then the algorithm is constructed in such a way that the first time-critical report is transmitted in the first half of the transmission time, thus in the first ½ second, and the second time-critical time-critical report is transmitted in the second half of the transmission time, thus in the second ½ second. The meaning of time-critical and time-uncritical navigation blocks will be further defined below.
An advantage of this further development is that the time-critical navigation data blocks can be completely received in a fraction 1/k of the transmission time of the time-uncritical navigation data blocks and can be processed in the terminal. Also, a more rapid emission of the time-critical navigation data blocks can take place, since it is possible to begin with the emission of data after the first time-critical navigation data blocks are available because the second time-critical navigation data block must first be present in the second fraction 1/k of the transmission time. It is analogous with additional time-critical navigation data blocks.
The navigation data blocks can be distributed into equal packets with indexed data addresses to perform the interleaving. An interleaving can then take place by successive transmission of one data unit of a packet in any given case. Thus, for example, any desired first data unit of the first packet is transmitted after distributing the data of the navigation data blocks, then any desired first data unit of the second packet, then any desired first data unit of the third packet etc. up to the last packet can be transmitted. Then a second data unit of the first packet is transmitted, then a second data unit of the second packet etc. is transmitted up to the last packet. This process is continued up to the last data unit of each packet.
In the aforementioned example, one proceeds from an arbitrary succession of emission of data units per packet. But an emission of data units per packet corresponding to the indexing of the data addresses of the packet can also take place. It can, therefore, be provided that first the data units of all packets with the lowest or highest data address are transmitted successively and then the data units of all packets with the next highest or next lowest data address are successively transmitted. If one represents the packet in the form of columns one beside the other so that the totality of the packets forms a matrix, then this type of emission corresponds to a line by line emission of the data units of the packet.
Indexed data addresses mean are herein defined such that corresponding data addresses of individual data packets for the data transmission system are recognizable through the addresses, that is, that especially the beginning and the end of the data packets are ascertainable, and that a succession of data within the data packets is defined. The type of indexing and addressing can basically be freely chosen in a suitable manner.
A further development of the invention provides that at least a first group of packets is reserved for packets of navigation data blocks with time-critical navigation data and at least a second group of packets is reserved for packets for navigation data blocks with time-uncritical navigation data. Thus not all types of navigation data are evenly distributed to data packets, but there is a differentiation according to the significance of the navigation data, especially according to time-critical aspects. A differentiated treatment of time-critical and time-uncritical navigation data in the framework of interleaving becomes possible, which offers advantages for additional processing of navigation data, as will be explained further below. Those data that are to be understood as time-critical data must be transmitted immediately to the terminals for a secure operation or for certain applications in the navigation terminals. Typical periods of time here are under one second. Time-uncritical data in contrast are data which the terminal requires for operation or certain uses, but which can arrive with a certain delay in the terminal without the operation of the terminal being basically disturbed. The ratios of the numbers of the packets which are reserved for time-critical and time-uncritical are preferably determined by the ratio of the volumes of time-critical data to time-uncritical data. If the volume of time-critical data is a fourth or a half of the volume of time-uncritical data, then a fourth or half of the packets are reserved for time critical data, the rest for time uncritical data.
It can be provided that status reports are transmitted as time-critical data and navigation useful data are transmitted as time-uncritical navigation data, whereby the navigation useful data are used directly for determining the position on the part of the navigation terminal. Identification data of system components, data on the version of certain software or even traffic information for land, water or air traffic or other types of status information can also be transmitted as status information data.
Integrity reports concerning navigation data transmitting facilities of the navigation system represent an important type of status information. These can be subjected to an interleaving with further navigation data by an interleaving process of the invention. The transmission of the navigation data preferably takes place through a navigation satellite of a satellite navigation system. Reports on the specific integrity of the transmitting navigation satellite or on the integrity of a selected group of navigation satellites, or on the integrity of all navigation satellites of a satellite navigation system to which the transmitting navigation satellite belongs are transmitted as integrity reports. Alternatively or additionally, it can be provided that reports on the integrity of navigation satellites of other satellite navigation systems are transmitted as integrity reports.
In one method of interleaving of time-critical and time-uncritical data, it is provided that                All packets have a length of n data units,        Packets of the first group of packets are filled with packets of n/k, k=2, 3, 4, 5 . . . data units of a navigation data block of time-critical material and        Packets of the second group of packets are filled with n data units of a navigation data block of time-uncritical data.        
All data packets thus possess the same length. A bit, a byte or another defined data symbol with defined symbol length can be provided as a data unit. The packets of the second group are simply completely filled with time-uncritical data of the corresponding navigation data blocks. If the end of a navigation data block with time-uncritical material is reached, the filling of packets which are reserved for time-uncritical data is continued with the next navigation data block of time-uncritical data.
Time-critical data are nonetheless processed differently: Packets for time-critical data are not filled up to the full length n with the data of time-critical data blocks, but only n/k data units of a packet are filled with data of a certain data blocks, in the simplest case, only the first half of the packet. The data content of the data block with time-critical data is therewith distributed in each case up to the first half of several packets. This provides a particular advantage. By interleaving, the data contents of the packet are transmitted in such a way that first all data units which stand at the beginning of the packet are successively transmitted. This is continued until the end of the packet is reached. One can easily recognize that a data block that was in any case distributed to the first half of several parameters was already completely transmitted after half of the time that is necessary for transmission of all data of all packets. It is similar for the general case of n/k data units with k=2, 3, 4 . . . Hence time-critical data can be very rapidly completely transmitted and nonetheless be subjected to interleaving. The whole number k can basically be freely defined. It preferably corresponds, however, to the number of data blocks with time-critical data which must be transmitted within a certain time unit.
In a preferred embodiment, the volume of time critical data is at a maximum of half, ideally a maximum of a fourth of the volume of data of the time-uncritical data. In this way, the effectiveness of the process is assured.
A further object of the present invention is a satellite navigation system with navigation satellites which on the one hand have facilities for furnishing navigation data in the form of several navigation data blocks, and on the other hand have facilities for transmitting data to navigation terminals. According to the present invention, each navigation satellite has a facility for interleaving at least two navigation data blocks prior to the transmission of navigation data to the navigation terminals.
The facility for interleaving can be further developed so that it is suited for implementing individual or all steps of an interleaving process as described above. The facility for interleaving is then suitably adapted to the corresponding steps of the interleaving process.
A further object of the present invention is a user terminal for a satellite navigation system. In accordance with the invention, the user terminal has a device for reconstruction of navigation data blocks which have been received by the user terminal by a receiving unit of at least one navigation satellite and which were subjected to an interleaving according to a previously described method prior to receiving. The corresponding device of the user terminal is thus constructed for recognizing the navigation data in the form described above and reconstructing the original navigation data blocks again on the basis of the original data through a de-interleaving complementary to the interleaving.
A further object of the present invention is a computer program for processing navigation data of a satellite navigation system which have been subjected to an interleaving according to one of the previously described methods, whereby the computer program is constructed for a cooperation with the facilities of an aforementioned user terminal. The computer program hence recognizes and processes the navigation data in the form described above and is able to reconstruct the original navigation data blocks again by a de-interleaving complementary to the interleaving.
A further object of the present invention is a computer program product includes a machine-readable program carrier on which an aforementioned computer program is stored in the form of electronically readable control signals, whereby the computer program product is constructed for interacting with a user terminal. The control signals can be stored in any suitable form. The electronic reading out can then correspondingly take place through electrical, magnetic, electromagnetic, electro-optical or other electronic methods. Examples for such program carriers are magnetic tapes, diskettes, hard disks, CD-ROM or semiconductor components.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.